Solarization of silver halide photographic emulsions

ABSTRACT

Silver halide is solarized by treatment with an aldehyde having more than one carbon atom or a ketone to provide direct positive photographic emulsions.

United States Patent Tagliafico et a1.

[ 5] Mar. 7, 1972 SOLARIZATION OF SILVER HALIDE PHOTOGRAPHIC EMULSIONS Inventors: Giovan Battista Tagliafico, Albisola Mare; Ferdinando Grazzino, Veneto, both of Appl. No.: 14,454

Foreign Application Priority Data Mar. 11, 1969 Italy ..35625 US. Cl ..96/45.2, 96/ 107 Int. Cl ..G03c 5/32 Field of Search ..96/l07, 45.2, 64

References Cited FOREIGN PATENTS OR APPLICATIONS 1,221,407 6/1960 France 1,405,108 5/1968 France OTHER PUBLICATIONS Mees, The Theory of Photographic Process, 3rd Ed. ed. 1966, Macmillan Co,

Primary Examiner-Norman G. Torchin Assistant ExaminerJohn L. Goodrow Attorney-Kinney, Alexander, Sell, Steldt & Delahunt [57] ABSTRACT Silver halide is solarized by treatment with an aldehyde having more than one carbon atom or a ketone to provide direct positive photographic emulsions.

9 Claims, 5 Drawing Figures PATENTEB A 972 3,647,458

sum 1 BF 3 l N VENTORS' mam/v5. 7464 MF/ca BYFEPDIIYHNOO' mzz/n/ 7 7' RAM-75 SOLARIZATION OF SILVER HALIDE PHOTOGRAPHIC EMULSIONS The present invention relates to photographic emulsions of the direct positive type and to a method for the preparation of such emulsions.

Light-exposed silver halide photographic emulsions blacken as the silver halide thereof is reduced to silver metal during development. Such blackening normally increases as the amount of light to which the emulsions have been exposed is increased. Increasing the exposure beyond a given amount, however, produces a decrease in the amount of blackening which occurs upon development. This reversal phenomenon is called solarization."

A solarized silver halide emulsion, i.e., an emulsion which has attained this reversal point, yields directly a positive image of a subject which is photographed, and accordingly is called a direct positive emulsion.

One known solarization process (German Pat. No. 693,917) involves exposing to a light source of suitable intensity a photographic emulsion obtained by precipitating silver halide in a gelatin solution. This process is performed prior to spreading of the emulsion on a support, and is difficult to carry out on an industrial scale because of the difficulty of uniformly exposing all the silver halide grains.

Another process (U.S. Pat. No. 2,005,837) comprises heating a silver halide emulsion in the presence of materials which promote fogging of the emulsion, such as AgNO decomposition product of animal or vegetable proteins, thiazoles, and photographic developers such as hydroquinone, paraphenylene diamine, amidol (diaminophenol hydrochloride), etc. Such treatments, however, may cause hydrolysis of the gelatin emulsion since, for example, the emulsion may require heating at 100 C. for half an hour or at 45 C. for -24 hours.

Another process (French Pat. Nos. 1,221,407 and 1,405,108) involves solarization of an emulsion by the addition thereto of formaldehyde. Formaldehyde, however, can cause irreversible coagulation of gelatin. Further, as formaldehyde is a volatile material, evaporation losses are likely to occur, resulting in poor reproducibility.

Briefly, the present invention provides a solarization process for silver halide which comprises treating silver halide with a solarizing agent selected from the group consisting of an aldehyde having more than one carbon atom and a ketone.

Such aldehydes and ketones may be aliphatic or aromatic, and may contain one or more aldehyde or ketone functions. The aldehydes and ketones of the aliphatic series, however, are generally more effective and hence are preferred. Especially preferred are those aldehydes and ketones which contain hydroxyl or halogen (e.g., chloro) substitution, since such substituted aldehydes and ketones have been found to be especially effective in solarizing silver halide emulsions. Glycol aldehyde, for example, is more effective than acetaldehyde, and monochloro acetone is more effective than acetone. The aldehydes of the present invention, of course, can be used also in the form of their bisulfite derivatives.

Aliphatic aldehydes which may be used in the present invention include, for example, acetaldehyde, chloral, glycol aldehyde, glyceraldehyde, glyoxal, glutaraldehyde, ribose, etc. Aromatic aldehydes include benzaldehyde, salicylaldehyde, terephthalic aldehyde, 3,5-dioxybenzaldehyde, 2,4-dioxybenzaldehyde (resorcylic aldehyde), 2,4,6-trioxybenzaldehyde (phloroglucinaldehyde), o-chloro-benzaldehyde, ooxy-p-chlorobenzaldehyde, etc. The aldehyde or ketone groups may also be found in a macromolecule, for example, the oxidized starch commercially available under the name of Sumstar" and manufactured by the Miles Chem. Co., Division of Miles Laboratories Inc. (U.S.A.).

Ketones useful in the present invention include acetone, monochloroacetone, acetylacetone, diacetyl (i.e., 2,3-butanone), sorbose, benzophenone, phenylacetone, 2,4-dihydroxy-benzophenone, etc.

The amount of solarizing agent which is utilized depends upon the method of preparation of the emulsion and upon the desired solarization effect. ln general, the contrast of the solarized emulsion increases as the amount of solarizing agent is increased. The solarizing agents of the present invention preferably are employed in an amount of from about 0.2 to about 500 mg. of solarizing agent per gram-atom of silver.

The solarizing treatment of the present invention, wherein silver halide is contacted with a solarizing agent, may be carried out at any stage of preparation of the emulsion. The solarizing agent maybe added all at once or in successive stages in the course of emulsion preparation. Preferably, however, the solarizing agent is added in solution during the silver halide precipitation step of the emulsion preparation.

The silver halides employed in the present invention include the chloride, the bromide, the iodide and mixtures thereof. The silver halide emulsions of the present invention may contain any of the hydrophilic, water-permeable colloids suitable for this purpose such as gelatin, hydrophilic polyvinyl copolymers, acrylamide polymers, polyvinyl alcohol. etc., and may contain the usual photographic additives such as coating aids and the like. The emulsions. may be coated on a wide variety of supports such as cellulose triacetate film, poly (ethylene terephthalate) film and other films, glass, paper, metal, etc., to provide photographic elements.

The present invention may be more easily understood by reference to the following illustrative examples. The graphs referred to in the examples are sensitometric curves for various emulsions wherein the ordinate D represents optical density and wherein the abscissa log E represents the logarithm of the exposure.

EXAMPLE 1 To a solution of gelatin 40 g. ammonium bromide 50 g. potassium iodide 3 g. glycol aldehyde, 2% \V/V water solution 2.5 ml. water 500 ml.

at 65 C. is added during 1 minute a solution of silver nitrate g. water 200 ml. cone. ammonia solution (13 M) 100 ml.

The whole is stirred at 65 C. for 30 minutes, and then a third solution of ammonium bromide 34 g. potassium iodide 1.0 g. water ml.

is added thereto over a period of 5 minutes.

The mass is stirred for additional 10 minutes at 65 C. and then the emulsion is adjusted to a pH of 3.0 by the addition of 45 percent sulfuric acid solution while cooling the whole to 30 C. At this point the silver salts and the gelatin are precipitated by the addition of a saturated solution of sodium sulfate.

The precipitate is washed with water and is redissolved at about 50 C. in a solution of 30 g. of gelatin in 600 ml. of water. After addition of the usual coating additives, the emulsion is spread on a transparent support and dried.

After exposure and development in a photographic developer for 5 minutes at 20 C a characteristic curve is obtained which is shown as Curve 1 in FIG. 1. For comparison, Curve ll of FIG. 1 represents data for the same emulsion prepared without the glycol aldehyde, and Curve lll represents data for this emulsion (without glycol aldehyde) prepared at 80 C. The solarization effect afforded by the glycol aldehyde far surpasses the effect afforded by preparing the emulsion at 80 C., thereby providing for higher maximum densities with less risk of hydrolysis.

EXAMPLE 2 To a solution of gelatin 35 g.

potassium bromide 60 g.

potassium iodide 1.5 g.

water 270 ml.

glyceric aldehyde. l% W/V water solution ml.

at 60 C. is added, over a period of 2 minutes, a solution of silver nitrate I00 g.

water l30-ml.

conc. ammonia solution (13 M) 100 ml.

which was previously heated to 60 C.

The whole is stirred for 25 minutes while carefully maintaining the temperature at 60 C. Thereafter, the following solution, preheated to 60 C., is added over a period of 3 minutes:

potassium bromide 42 g. potassium iodide 06 gv water 100 ml:

The whole is kept at 60 C. for minutes and the pH is adjusted to a value of 3.0. The emulsion preparation is then continued as in Example 1.

Curve I of FIG. 2 represents the characteristic curve obtained with this emulsion. Curve II OF FIG. 2 represents the characteristic curve obtained from the same emulsion prepared without the use of glyceric aldehyde.

EXAMPLES 3-9 The emulsion of Example I was duplicated except that equimolar amounts of the following aldehydes were substituted for glycol aldehyde: (FIG. 3)

Example 3acetaldehyde in the emulsion (Curve I) Example 4acetaldol in the emulsion (Curve II) Example 5pyruvaldehyde in the emulsion (Curve III) Example 6ribose in the emulsion (Curve IV) Example 7-glyoxal in the emulsion (Curve V) Example 8-glutaraldehyde in the emulsion (Curve VI) Example 9bisuliite-glutaraldehyde complex in the emulsion (Curve VII) In FIG. 3 the characteristic curves obtained from the different emulsions are shown. Curve No. VIII refers to the emulsion prepared without the addition of solarizing agents.

EXAMPLES lO-l2 The emulsion of Example I was duplicated except that equimolar amounts of the following aldehydes were substituted for glycol aldehyde: (FIG. 4)

Example lO-benzaldehyde for the emulsion (Curve I) Example I I-salicylaldehyde for the emulsion (Curve II) Example l2-phloroglucinaldehyde for the emulsion (Curve III) The characteristic curves obtained from these emulsions are shown in FIG. 4 Curve IV refers to the emulsion prepared without the addition of solarizing agents.

EXAMPLES l3-l9 Example l8be nzophenone for the emulsion (Curve VI) Example l9d|acetyl (2.3-butanone) for the emulsion (Curve VII) In FIG. 5 the sensitometric curves obtained from such emulsions are shown. Curve No. VIII corresponds to the emulsion prepared without the addition of ketones.

What is claimed is:

1. In the process of solarization wherein a silver halide emulsion is treated with a solarization agent the improvement wherein, said material is selected from the group consisting of an aldehyde having more than one carbon atom and a ketone.

2. In the process for preparing a direct positive silver halide photographic emulsion, the step which comprises treating silver halide during preparation of said emulsion with a solarizing agent which is an aldehyde having more than one carbon atom or a ketone.

3. The process of claim 2 wherein said treatment is carried out during precipitation of silver halide in said emulsion.

4. The process of claim 2 wherein said emulsion is treated with from about 0.2 to about 500 mg. of said solarizing agent per gram-atom of silver. I l

5. The process of claim 2 wherein said solarizing agent is an aldehyde having more than one carbon atom and which contains a halide or hydroxyl substituent.

6. The process of claim 5 wherein said solarizing agent is glycol aldehyde.

7. The process of claim 5 wherein said solarizing agent is glyceraldehyde.

8. A silver halide photographic emulsion solarized by the process of claim 2.

9. In the process for preparing a direct positive silver halide photographic emulsion, the step which comprises treating silver halide during preparation of said emulsion with a solarizing agent selected from the group consisting of an aldehyde having more than one carbon atom and a ketone, said solarizing agent containing hydroxyl or halogen substitution. 

2. In the process for preparing a direct positive silver halide photographic emulsion, the step which comprises treating silver halide during preparation of said emulsion with a solarizing agent which is an aldehyde having more than one carbon atom or a ketone.
 3. The process of claim 2 wherein said treatment is carried out during precipitation of silver halide in said emulsion.
 4. The process of claim 2 wherein said emulsion is treated with from about 0.2 to about 500 mg. of said solarizing agent per gram-atom of silver.
 5. The process of claim 2 wherein said solarizing agent is an aldehyde having more than one carbon atom and which contains a halide or hydroxyl substituent.
 6. The process of claim 5 wherein said solarizing agent is glycol aldehyde.
 7. The process of claim 5 wherein said solarizing agent is glyceraldehyde.
 8. A silver halide photographic emulsion solarized by the process of claim
 2. 9. In the process for preparing a direct positive silver halide photographic emulsion, the step which comprises treating silver halide during preparation of said emulsion with a solarizing agent selected from the group consisting of an aldehyde having more than one carbon atom and a ketone, said solarizing agent containing hydroxyl or halogen substitution. 